Among recent Haitian emigrants living in Miami the prevalence of serum antibodies to HTLV-III/LAV is 2-9%. Haitian-born women deliver between 2200 and 2500 infants annually at Jackson Memorial Hospital in Miami; approximately 20 of these infants will develop clinical evidence of HTLV-III/LAV infection each year. These deliveries constitute at least 90% of all births among Haitian emigrants in Dade County. We propose to determine the proportion of seropositive mothers that give birth to seropositive, virus-positive infants that develop clinical syndromes associated with HTLV-III/LAV infection. Seropositive and seronegative infants of seropositive mothers will be followed with a comparable number of seronegative infants of seronegative mothers for two years to assess their outcome. Information obtained from this population-based study will be of significance in two major areas. First, the information from the mothers will be used to assess the risks to unborn infants of women with HTLV-III/LAV infection. Second, the population-based character of the study will provide more complete information on the clinical spectrum of HTLV-III/LAV infection among infants in this population.